Snow inhaled the drug from a plastic container, and soon became "woozy" before being led to an MRI machine to have his brain activity analysed.

Snow went to "the darkest mental place I have ever been"

Inside the machine, he becomes increasingly anxious, saying "I don't think I want to do this, it's horrible. Can you let me out?"

Once released from the machine, Snow is visibly distressed and dazed. Alluding to his reporting from war zones, Snow says "If you can stick it out in Gaza, you should be able to stick it out in a bloody scanner."

He wrote on his Channel 4 website blog that the effects were so strong he forgot he was even being filmed:

By the time I was completely stoned I felt utterly bereft. I felt as if my soul had been wrenched from my body. There was no one in my world. I felt I had lost all control and had only the vaguest awareness of who I was and what on earth I was doing. I cascaded into a very, very, dark place, the darkest mental place I have ever been.

I was frightened, paranoid, and felt physically and mentally wrapped in a dense blanket of fog. I lost all sense that I was being filmed by Channel 4.

....

I’ve worked in war zone but I’ve never been as overwhelmingly frightened as I was right then – and as I emerge from the scanner you see me blearily sitting up and hugging young Dr Rebecca for my dear life, as if she was my mother.

Snow - who said he had smoked regular hash cannabis before - described the drug as "aggressive filth" that "robbed" him of his persona.

The full programme, 'Drugs Live: Cannabis on trial', will be shown on 3 March on Channel 4.

Snow in the MRI scanner

Snow says he doesn't yet know what his ordeal contributed to the show, but that there are other "guinea pigs" who will also appear.

He concludes: "If many who smoke this stuff had ever seen the physical effects on the brain as displayed through the MRI scanner, they would make a more informed judgement as to what they were doing."